The present invention relates to a variable displacement compressor for vehicle air-conditioning systems.
In a prior art compressor shown in FIGS. 6 and 7, a housing 102 includes a crank chamber 101, and a drive shaft 103 is rotatably supported by the housing 102. A rotor 104 is secured to the drive shaft 103 in the crank chamber 101. A drive plate, or a swash plate 105, is supported by the drive shaft 103 to slide axially and to incline with respect to the axis L. A hinge mechanism 106 couples the rotor 104 to the swash plate 105. The swash plate 105 integrally rotates with the drive shaft 103 through the hinge mechanism 106.
A cylinder block 108 constitutes part of the housing 102. A plurality of cylinder bores 108a (six in the compressor of FIG. 7) are formed in the cylinder block 108. The cylinder bores 108a are arranged on a circle about the axis L of the drive shaft 103 at equal intervals. A piston 107 is accommodated in each cylinder bore 108a. Each piston is coupled to the swash plate 105 through a pair of shoes 115. When the drive shaft 103 is rotated, the swash plate 105 is rotated through the rotor 104 and the hinge mechanism 106. The rotation of the swash plate 105 is converted into reciprocation of each piston 107 in the corresponding cylinder bore 108a through the shoes 115.
A thrust bearing 109 is located between the rotor 104 and an inner wall 102a of the housing 102. The thrust bearing 109 includes rollers 109a and a pair of ring-shaped races 109b. The rollers 109a are arranged about the axis L of the drive shaft 103 and are held between the pair of races 109b. Each roller extends radially. The thrust bearing 109 receives a compression force applied to the rotor 104 from the pistons 107 through the swash plate 105 and the hinge mechanism 106.
A discharge chamber 120 is connected to the crank chamber 101 through a pressurizing passage 110. A displacement control valve 111 is provided in the pressurizing passage 110. The control valve 111 adjusts the opening size of the pressurizing passage 110 and controls the flow rate of refrigerant gas fed to the crank chamber 101 from the discharge chamber 120. This varies the difference between the pressure in the crank chamber 101 and the pressure in the cylinder bores 108a. The inclination angle of the swash plate 105 is varied in accordance with the pressure difference through the hinge mechanism 106, which controls the displacement of the compressor.
The control valve 111 includes a valve body 112, a solenoid 113, and a pressure sensitive mechanism 114. The valve body 112 opens and closes the pressurizing passage 110. The solenoid 113 urges the valve body 112 toward its closed position. The pressure sensitive mechanism 114 operates the valve body 112 in accordance with the pressure (suction pressure) in a suction chamber 121. The valve body 112 is operated by the pressure sensitive mechanism 114 and the solenoid 113 to vary the opening size of the pressurizing passage 110.
When the cooling load is great, the electric current supplied to the solenoid 113 is increased, which increases a force urging the valve body 112 to reduce the opening size of the pressurizing passage 110. In this case, the pressure sensitive mechanism 114 operates the valve body 112 to lower a target value of the suction pressure. In other words, the control valve 111 adjusts the displacement of the compressor so that a lower suction pressure is maintained by increasing the current supply to the solenoid 113.
When the cooling load is small, the supply of electric current to the solenoid 113 is decreased, which decreases the force urging the valve body toward its closed position. In this case, the pressure sensitive mechanism 114 operates the valve body 112 to raise the target value of the suction pressure. In other words, the control valve 111 adjusts the displacement of the compressor so that a higher suction pressure is maintained decreasing the electric current supplied to the solenoid 113.
As shown in FIG. 6, the swash plate 105 includes a point D1 corresponding to the top dead center position of each piston 107 and a point D2 corresponding to the bottom dead center position of each piston 107. In FIG. 6, the upper piston 107 is positioned at the top dead center by the swash plate 105 corresponding to point D1, and the lower piston 107 is positioned at the bottom dead center by the part of the swash plate 105 corresponding to point D2. The hinge mechanism 106 is axially aligned with point D1.
As shown in FIG. 7, each piston 107 located on the part of the swash plate 105 ranging from point D1 to point D2 in the rotational direction (clockwise) of the swash plate 105 is performing a compression stroke, in which the piston moves from the bottom dead center to the top dead center. In the compression stroke, a compression reaction force applied to each piston 107 pushes the swash plate 105 toward the rotor 104. On the other hand, each piston located on the part of the swash plate 105 ranging clockwise from point D2 to point D1 in FIG. 7 is performing a suction stroke, in which the piston 107 moves from the top dead center to the bottom dead center. During the suction stroke, the negative pressure in the cylinder bore 108a causes the piston to pull the swash plate 105.
Thus, the direction of the forces applied to the part of the swash plate 105 corresponding to the pistons 107 performing compression strokes is opposite to that of the forces applied to the part of the swash plate 105 corresponding to the pistons 107 performing suction strokes. Therefore, as shown in FIG. 7, a resultant force F of the forces applied to the swash plate 105 from the pistons 107 is offset from the axis L of the drive shaft 103. Accordingly, a moment based on the resultant force F is applied to the rotor 104, and the moment inclines the rotor 104 with respect to a plane perpendicular to the axis L of the drive shaft 103.
The control valve 111 operates the valve body 112 using the pressure sensitive mechanism 114 and the solenoid 113 to adjust the displacement of the compressor. The compressor shown in FIG. 6 can vary the compression ratio, which is the ratio of the discharge pressure to the suction pressure. For example, when the supply of electric current to the solenoid 113 is increased, which lowers the target suction pressure, the displacement is maximized by the pressure sensitive mechanism 114, and this increases the compression ratio. In contrast, when the supply of the electric current to the solenoid 113 is decreased, which raises the target suction pressure, an intermediate displacement is set by the pressure sensitive mechanism 114, and this decreases the compression ratio.
The location of the resultant force F applied to the swash plate 105 from the pistons 107 varies radially. As shown in FIG. 7, the resultant force F can be located further from the axis L than an effective reception radius r1. The effective reception radius r1 is the radius of a circle defined by the outer-most points of contact between the rollers 109a and the races 109b. A force applied at a location within the effective reception radius r1 is directly transferred to the housing by the thrust bearing 109.
The phenomenon that the position of the resultant force F varies radially from the effective reception radius r1 was discovered through an experiment performed by the present inventors. In the experiment, when the compression ratio was lowest, the location of the force F extended to a radius r2, which is the radius of the axis S of the pistons 107. Accordingly, the resultant force F applied to the swash plate 105 is not directly received by the thrust bearing 109 through the rotor 104. Therefore, an inclination moment based on the resultant force F inclines the rotor 104, which increases the clearance between the housing 102 and one side of the bearing. As a result, the thrust bearing 109 is subject to chattering, which causes noise and vibration.
The present invention relates to a variable displacement compressor having a thrust bearing that can directly receive the force applied to a drive plate from pistons.
To achieve the above objective, the present invention provides a variable displacement compressor having the following structure. A housing defines a crank chamber, a suction chamber and a discharge chamber. A drive shaft is rotatably supported in the housing. A plurality of cylinder bores are formed in the housing. Each cylinder bore is arranged on a circle which center is the axis of the drive shaft. A plurality of pistons are accommodated in the cylinder bores. A drive plate is coupled to the piston for converting rotation of the drive shaft to reciprocation of the piston. The drive plate inclines and slides axially along the drive shaft, which varies the piston stroke to change the displacement of the compressor. A control valve controls pressure in the crank chamber to change the inclination of the drive plate. The control valve includes a valve body, an electric drive means for applying force to the valve body corresponding to the value of the current fed to the electric drive means. A rotor is mounted on the drive shaft to rotate integrally with the drive shaft. A hinge mechanism is located between the rotor and the drive plate. The hinge mechanism rotates the drive plate integrally with the rotor and for guiding the motion of the drive plate. A thrust bearing is located between the rotor and the housing. The thrust bearing receives a resultant force of the pistons through the rotor and the hinge mechanism. An effective reception radius, which is defined by an outermost load-bearing point of the thrust bearing, is greater than the distance from the axis of the drive shaft to the axis of any one of the pistons.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.